Project Leader: Alain Charest. Extracellular RNA (exRNA) is a newly discovered form of cellular communication whereby information from one cell to another is conveyed by RNA molecules. exRNAs are protected from extracellular RNases by encapsulation within membrane vesicles or as amalgamations of RNA and proteins complexes (ribonucleoproteins RNPs). It appears that the production of these entities is not random and is the result of a highly orchestrated machinery, the details of which remain ill-defined. In this proposal, we aim to uncover the molecular mechanisms by which exRNA is encapsulated in extracellular vesicles and RNPs and how therapeutic interventions affect these mechanisms using glioblastoma multiforme (GBM) as a model system. Using genetically engineered mouse models of GBM that are driven by overexpression and activation of EGFR and PDGFRa, the two most common.genetic events found in GBM, we will determine the vesicle and RNP exRNA profiles of EGFR GBMs and PDGFRa GBMs using deep sequencing methods. Once established, we will then study the effect of therapeutic treatment on the dynamics of exRNA production and perform functional studies of exRNA on target cells in vitro and in vivo. We will initially focus on miRNA as it has been shown that miRNA make up a significant proportion of exRNA. Our project relates to the other projects in this U19 application on multiple levels. We will work in close collaboration with Dr. Anna Krichevsky on deciphering and cataloging the exRNA sequence composition of our genetically-defined glioblastoma tumor cells. We will also collaborate with Dr. Stephen Gould on the molecular mechanisms of exRNA production in glioblastoma as a function of EGFR and PDGFRa signaling pathways and with Dr. Xandra Breakefield on the development of methods and reagents to study exRNA transfer to recipient cells. Finally, we will work closely with Dr. Thorsten Mempel who will provide intravital imaging technology to evaluate and study exRNA fluorescent reporters in vivo.